The present invention relates generally to the field of telecommunications and, in particular, to a technique for tuning a cavity filter based on position measurements for tuning members.
Wireless telecommunications systems transmit signals between users using radio frequency (RF) signals. A typical wireless system includes a plurality of base stations that are connected to the public switched telephone network (PSTN) via a mobile switching center (MSC). Each base station includes a number of radio transceivers that are typically associated with a transmission tower. Each base station is located so as to cover a geographic region known colloquially as a xe2x80x9ccell.xe2x80x9d Each base station communicates with wireless terminals, e.g. cellular telephones, pagers, and other wireless units, located in its geographic region or cell.
A wireless base station includes a number of modules that process RF signals. These modules typically include, by way of example, mixers, amplifiers, filters, transmission lines, antennas and other appropriate circuits. One type of filter that finds increased use in wireless base stations is known as a cavity filter.
Cavity filters typically include a plurality of resonators located in a housing. The frequency response of each resonator is adjusted using a tuning member, e.g., a tuning screw, that extends through a plate of the housing into the cavity of the resonator. A group of resonators coupled in series form a filter with a specified overall frequency response.
During manufacturing, each filter is tuned to provide the specified frequency response. A technician tunes the filter by adjusting the position of the tuning members in the plate for each resonator of the filter in an iterative process until the correct frequency response is achieved. This can be a tedious and time-consuming process. Further, the process is labor intensive and relies on the ability of skilled artisans to accomplish the desired tuning in a reasonable amount of time. It can take years for a technician to reach a productive level of skill in tuning these filters. Moreover, the process often requires design and use of various mechanical jigs. Finally, filters are tuned on a one-by-one basis when fully assembled.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a technique for tuning filters in a less labor intensive manner.
The above mentioned problems with tuning cavity filters and other problems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention provide for pre-tuning a cavity filter using measured positional data for a plurality of tuning members of a tuned cavity filter. Advantageously, embodiments of the present invention allow a low-skilled technician to pre-tune an assembled cavity filter within a close approximation of a desired frequency response in a short period of time without the use of costly, complex mechanical jigs, and without monitoring signals processed by the filter.
In one embodiment, a method for tuning a cavity filter is provided. The cavity filter includes a plurality of tuning members. The method includes selecting a stored set of positional values for the tuning members, driving the tuning members of the cavity filter to the stored set of positional values, and further adjusting the position of the tuning members as necessary to achieve a desired frequency response for the cavity filter.